The term grey goo is usually used in a science fiction or popular-press context. In the worst postulated scenarios (requiring large, space-capable machines), matter beyond Earth would also be turned into goo (with goo meaning a large mass of replicating nanomachines lacking large-scale structure, which may or may not actually appear goo-like). The disaster is posited to result from a deliberate doomsday device, or from an accidental mutation in a self-replicating nanomachine used for other purposes, but designed to operate in a natural environment.

Risks and precautions

It is unclear whether the molecular nanotechnology would be capable of creating grey goo at all. Among other common refutations, theorists suggest that the very size of nanoparticles inhibits them from moving very quickly. While the biological matter that composes life releases significant amounts of energy when oxidised, and other sources of energy such as sunlight are available, this energy might not be sufficient for the putative nanorobots to out-compete existing organic life that already uses those resources, especially considering how much energy nanorobots would use for locomotion. If the nanomachine was itself composed of organic molecules, then it might even find itself being preyed upon by preexisting bacteria and other natural life forms.

If self-replicating machines were built of inorganic compounds or made much use of elements that are not generally found in living matter, then they would need to use much of their metabolic output for fighting entropy as they purified (reduce sand to silicon, for instance) and synthesized the necessary building blocks. There would be little chemical energy available from inorganic matter such as rocks because, aside from a few exceptions, it is mostly well-oxidized and sitting in a free-energy minimum.

Assuming a molecular nanotechnological replicator were capable of causing a grey goo disaster, safety precautions might include programming them to stop reproducing after a certain number of generations (see cancer), designing them to require a rare material that would be sprayed on the construction site before their release, or requiring constant direct control from an external computer. Another possibility is to encrypt the memory of the replicators in such a way that any changed copy would decrypt to a meaningless, random bit string.

Drexler more recently conceded that there is no need to build anything that even resembles a potential runaway replicator. This would avoid the problem entirely. In a paper in the journal Nanotechnology, he argues that self-replicating machines are needlessly complex and inefficient. His 1992 technical book on advanced nanotechnologies Nanosystems: Molecular Machinery, Manufacturing, and Computation describes manufacturing systems that are desktop-scale factories with specialized machines in fixed locations and conveyor belts to move parts from place to place. Popular culture, however, remains focused on imagined scenarios derived from his older ideas. None of these measures would prevent a party creating a weaponised grey goo, were such a thing possible.

Oxford based philosopher Nick Bostrom discusses the idea of a future powerful superintelligence, and the risks that we/it face should it attempt to gain atomic level control of matter.

In Britain, the Prince of Wales called upon the Royal Society to investigate the "enormous environmental and social risks" of nanotechnology in a planned report, leading to much delighted media commentary on grey goo. The Royal Society's report on nanoscience was released on 29 July2004, and dismisses the idea as impossible.

More recent analysis has shown that the danger of grey goo is far less likely than originally thought. However, other long-term major risks to society and the environment from nanotechnology have been identified. Drexler has made a somewhat public effort to retract his grey goo hypothesis, in an effort to focus the debate on more realistic threats associated with knowledge-enabled nanoterrorism and other misuses.

Famous quotes

Grey goo in science fiction

In Frank Herbert's Dune series, a weapon is being researched at one point which would be "a self improving thing which would seek out life and reduce that life to its inorganic matter." Though not nanotechnological in nature, the autonomous but unthinking threat is similar.

In Wil McCarthy's sci-fi novel Bloom, Earth's ecosystem is destroyed within hours by a grey goo, annihilating all biological life. The grey goo then develops its own unique "ecosystem." The only human survivors are colonists who flee to the outer solar system. The book's protagonists come from Jupiter's moonGanymede.

Although not strictly speaking science fiction, Jasper Fforde's Lost in a Good Book features a narrowly-averted apocalypse in which all biological life in the world would be converted into "Dream Topping" (a whipped cream-like substance) by overenthusiastic nanomachines.

In the intro to the video game Deus Ex: Invisible War, a villain uses a nanite detonator, wiping out the entire city of Chicago with a goo-like substance that seems to freeze/destabilize anything it comes into contact with.

Self-reproducing nanorobots were heavily featured in Michael Crichton's novel Prey.

In Greg Bear's novel Blood Music, simple biological computers evolve to become self-aware "noocytes," which assimilate most of the biosphere of North America before abandoning the normal plane of existence.

In Walter Jon Williams' novel Aristoi, Earth was destroyed by grey goo (codenamed "Mataglap") and it is used to destroy an asteroid installation owned by the protagonist.

In the made-for-TV film Path of Destruction, accidentally released grey goo causes weather problems.

In John Robert Marlow's novel Nano, the invention of self-replicating nanites results in a team of assassins hired by the government on the hunt for a scientist and reporter, nearly ending in the destruction of San Francisco by "incorrectly programmed" grey goo.

In Gargoyles episode "Walkabout," a sentient nanite swarm called "The Matrix" is confronted in the Australian outback.

In Moonseed, the 1998 book by Stephen Baxter, the Earth is consumed by a grey goo-type substance inadvertently imported from the Moon.

In the game Outpost 2, the faction of Eden is experimenting on a way to terraform the new planet they have settled to support life. Suddenly the experiment goes horribly wrong and a nanotechnology/terraforming virus is released, eventually taking over the planet and causing the survivors to work together in order to build a new spacecraft to leave the planet to find a new one.

In the BBC's 2005 version of Quatermass, a brief reference is made to grey goo as the scientists watch the rapid reproduction of spores under a microscope.

In the Justice League Unlimited episode "Dark Heart," many of the Leaguers fight the eponymous ever-expanding entity. Created from technology of another planet to attack and quickly destroy their enemies, the Dark Heart turned against the own planet which created it, due to it not knowing that the war was over. With both planets annihilated, the entity traveled the universe until eventually reaching the Earth. However, it was destroyed by The Atom, who caused a "heart attack" of sorts to stop the Dark Heart from feeding itself on the dark matter which, aside from serving as its blood, allowed it to replicate at astonishing speeds. Unable to endure such a critical condition, the Dark Heart exploded, stopping its self-replication for good.

In the TV series Lexx, the universe is completely transformed into "one-armed Mantrid drones", which are considerably larger than nanotechnology. Luckily, there's still a parallel universe.